The diets of the White-headed Duck Oxyura
leucocephala, Ruddy Duck O. jamaicensis and
their hybrids from Spain
MARTA I. SANCHEZ1, ANDY J. GREEN1* and J. CARLES DOLZ
2
1Estación
Biológica de Doñana, Avenida de María Luisa s/n, Pabellón del Perú, 41013 Sevilla, Spain and
2Consellería de Agricultura y Medio Ambiente, C/. Churruca 29, 03071 Alicante, Spain
We studied the gut contents of 17 White-headed Ducks, 25 North American
Ruddy Ducks and 26 hybrids between the two species collected from 14 Spanish
wetlands. This is the most detailed study to date of Oxyura diet in the
Palearctic region. Food items from at least 27 families of in ertebrates and at
least ten families of a uatic plants were identified. The method of collection of
ducks and rapid digestion of soft-bodied in ertebrates may ha e o erestimated
the importance of plant matter. owe er, animal foods were more important,
constituting 7 % of aggregate olume of gullet contents. n both duck
species and their hybrids, benthic chironomid lar ae and pupae were the
most important food item, present in 69% of gullets and 75% of gizzards, and
constituting 5% of aggregate olume and 26% of aggregate percentage in
gullets. Angiosperm seeds were the next most important dietary component,
and crustaceans (mainly Amphipoda, Cladocera and sopoda) and green plant
material were of secondary importance. No significant differences in diet were
detected between duck species, sex or age classes. Birds sampled in the breeding
season had more nematodes, but these may ha e been parasitic. Chironomids
were less abundant in Ruddy Ducks collected from northern Spain outside of
the range of the White-headed Duck.
The White-headed Duck Oxyura leucocephala is
the only stifftail (Oxyurini) native to the
Palearctic. It is a globally threatened species
with a fragmented distribution and a declining
world population.1,2 In Spain, numbers
increased from 22 birds in 1977 to 1453 in 1999
in response to conservation measures.3,4 The
most important threat to the Spanish population is the spread of the North American
Ruddy Duck O. jamaicensis jamaicensis introduced to northern Europe and now expanding
into the range of its congener.1,5 In Spain,
Ruddy Ducks produce fertile hybrids with the
White-headed Ducks and both Ruddy Ducks
and hybrids are shot by governmental conservation organizations to counter genetic
integration.5—7
*Correspondence author.
Email: andy@ebd.csic.es
Here, we analyse the stomach contents of
White-headed Duck, Ruddy Duck and their
hybrids shot or found dead in Spain. We
present the most detailed study to date of
Oxyura diet in the Palearctic region, and look
for variation in diet with sex, age, season or
geographical region.
MATERIAL AND METHODS
We studied 25 Ruddy Ducks and 26 hybrids
shot during a control programme organized by
the Spanish regional and national government
administrations7 at 14 wetlands across Spain at
different times of the year, from 14 March 1992
to 17 February 1998 (Figs 1 & 2). Similarly,
17 White-headed Ducks were collected
between 19 November 1985 and 28 July 1998
(Figs 1 & 2), 16 of them after 12 March 1992. Six
birds were shot incidentally during a Ruddy
13
12
11
10
9
4 21 3
5 6
7
8
Figure 1. Location of autonomous communities and wetlands where stifftails were collected in Spain. Wetlands
1–11 marked with circles are within the range of the
White-headed Duck. Numbers of birds (L, White-headed
Duck; J, Ruddy Duck; H, hybrid) collected at each wetland are as follows. Andalucía: 1, Veta la Palma, Isla
Mayor, Sevilla, H (6), J (1); 2, Lucio del Cangrejo Grande,
S 99/50
1 Sevilla, J (1); 3, Lagunas de
Parque
NaturalFig
de Doñana,
La Lantejuela, Sevilla, L (2); 4, Marismas de El Rocío,
Huelva, L (1); 5, Laguna de Tarelo, Sanlúcar de
Barrameda, Cádiz, H (3), J (2); 6, Laguna de Medina,
Jerez de la Frontera, Cádiz, J (1); 7, Lagunas de Puerto
Real, Cádiz, J (1); 8, Parque Natural Punta EntinasSabinar and nearby, Almería, J (1). Valencia: 9, El
Hondo, Elche, Alicante, J (8), H (12), L (12); 10, Cullera,
Valencia, L (1). Castillala Mancha: 11, Dehesa de
Monreal, Huerta de Valdecarábanos, Toledo, H (1).
Aragón: 12, Laguna de Sariñera, Sariñera, Huesca, J (1).
País Vasco: 13, Ullibarri-Gamboa, Álava, J (7).
Cantabria: 14, Marisma de Santoña, J (1).
Duck control programme. Two individuals
were shot illegally and confiscated, whilst
another nine were found dead (from lead
poisoning, Salmonella or botulism).
Treatment of birds varied considerably in
this heterogeneous sample, involving many
organizations and people. Most were frozen
shortly after collection, then sent to the Doñana
National Park or Doñana Biological Station for
necropsy. Birds were sexed and aged (adults or
juveniles) based on plumage characteristics,
gonad inspection and presence or absence of
the bursa of Fabricius. We analysed separately
the gullet (oesophagus plus proventiculus) and
gizzard, which were stored in 50% alcohol after
thawing. Unfortunately, for many individuals,
the contents of the oesophagus and proventiculus were either discarded or mixed together
before we could analyse them. Foods were
© 2000 British Trust for Ornithology, Bird Study, 47, 275–284
sorted and identified to the lowest possible
taxonomic level using keys.8—18
Volumetric measurement of individual food
items in the gullet was expressed as the mean
of volumetric percentages (aggregate percent)
and percentage of total volume (aggregate
volume).19 The percent occurrence (i.e. the
percentage of individual ducks in which each
food item was recorded) was calculated separately for gullet and gizzard samples. We also
calculated an Index of Relative Importance (IRI).a
The percent occurrence of different food
items in the gizzard was compared between
categories of stifftail using χ2 and Fisher ’s exact
tests (the latter when expected values fell below
five in 2 x 2 contingency tests). Birds collected
9
a
Hybrids
Ruddy Ducks
White-headed Ducks
8
7
6
5
4
3
Number of individuals
14
2
1
0
14
b
12
10
8
6
4
2
0
J
F M A M J
J
A S O N D
Month
Figure 2. Number of (a) gullet and (b) gizzard samples
for each stifftail taxon collected in different months.
Diet of Oxyura in Spain
in the breeding season (considered as April to
September inclusive) were compared with
those from the non-breeding season (October to
March). Ruddy Ducks collected in northern parts
of Spain outside the range of the White-headed
Duck (Fig. 1)3,20 were compared with Ruddy
Ducks and hybrids collected further south.
RESULTS
The animal food items identified in the stifftail
277
gullets and gizzards represented a broad range
of aquatic invertebrates from at least 27 families
(Appendix 1). Seeds were identified from ten
families of aquatic plants (Appendix 1). Large
numbers of seeds could not be identified, and
most of these were from terrestrial plants.
Although food items in the gullet were more
intact and easier to identify, a broader range of
invertebrates were identified in the gizzards,
due to larger sample size (Table 1). There were
no significant differences between stifftail taxa
Table 1. Percentage occurrence of different food items in the gullet (A) and gizzard (B) of stifftails in Spain.
All combined
Plant
Angiosperm seeds
Charophyta (oospores)
Green plant material
Animal1
Bryozoa
Nematoda
Polychaeta
Oligochaeta
Achaeta
Mollusca
Gastropoda
Bivalvia
Crustacea
Ostracoda
Cladocera
Copepoda
Decapoda
Isopoda
Amphipoda
Unidentified
Arachnida
Acarina
Insecta
Odonata
Corixidae
Aphididae
Ceratopogonidae
Chironomidae, larvae
Chironomidae, pupae
Other Diptera
Formicidae
Coleoptera
Unidentified insects
Unident. invertebrates
A
(29)
B
(68)
82.76
75.86
10.34
48.28
96.55
10.34
–
3.45
3.45
–
98.53
97.06
16.18
79.41
94.12
7.35
11.76
10.29
1.47
2.94
10.34
–
White-headed Duck
A
(6)
Ruddy Duck
Hybrids
A
(8)
B
(26)
100
96
16
80
100
16
4
8
4
4
87.5
87.5
12.5
50
87.5
12.5
–
12.5
12.5
–
100
100
26.92
80.77
100
3.85
3.85
19.23
–
3.85
6.67
–
20
20
25
–
30.77
19.23
5.88
17.65
–
–
–
5.88
5.88
26.67
20
–
26.67
6.67
–
–
16
32
–
–
4
12
12
37.5
25
–
–
12.5
25
–
11.54
38.46
3.85
7.69
–
11.54
7.69
–
–
–
–
–
3.85
–
–
–
–
66.67
16.67
–
–
–
50
–
5.88
11.76
–
5.88
58.82
35.29
–
5.88
41.18
52.94
23.53
6.67
13.33
6.67
–
73.33
40
6.67
6.67
26.67
60
6.67
20
32
–
16
68
48
8
4
48
72
16
–
12.5
–
–
50
50
–
–
12.5
37.5
–
11.54
7.69
–
7.69
84.62
53.85
11.54
3.85
38.46
46.15
15.38
B
(17)
A
(15)
100
83.33
–
66.67
100
–
–
–
–
–
94.12
94.12
–
76.47
76.47
–
35.29
–
–
–
73.33
66.67
13.33
40
100
13.33
–
–
–
–
22.06
14.71
–
–
11.76
–
27.59
17.24
–
13.79
6.9
6.9
–
11.76
30.88
1.47
2.94
1.47
10.29
8.82
16.67
–
–
–
–
–
–
–
1.47
3.45
10.34
3.45
–
65.52
37.93
3.45
3.45
17.24
51.72
3.45
13.24
17.65
–
10.29
72.06
47.06
7.35
4.41
42.65
57.35
17.65
B
(25)
Values in parentheses = n
1 Excludes nematodes since they may not be food items, see text.
© 2000 British Trust for Ornithology, Bird Study, 47, 275–284
Downloaded by [CSIC Biblioteca] at 04:30 07 February 2012
278
M.I. Sanchez, A.J. Green and J.C. Dolz
in the percent occurrences of food categories
in the gizzards (Table 1). However, a lower
diversity of invertebrates was recorded in
White-headed Ducks (Table 1). There were no
significant differences in percent occurrence
between males (n = 44) and females (n = 15) or
adults (n = 33) and immatures (n = 22). The
only significant difference between samples
from the breeding (n = 24) and non-breeding
(n = 42) seasons was that nematodes were
absent in the non-breeding season but present
in 29% of gizzards in the breeding season
(Fisher ’s exact test: P < 0.001). Chironomids
were recorded from 33% of gizzards in Ruddy
Ducks from northern areas (n = 9), compared
with 88% of Ruddy Ducks or hybrids from the
south (n = 42, Fisher ’s exact test: P = 0.0016).
The complete absence of charophyte oospores,
Odonata, amphipods and polychaetes from
northern samples was noteworthy, although
not statistically significant.
In general, the aggregate percents and
aggregate volumes of different foods recorded
in gullets were similar between stifftail taxa,
with Chironomidae and angiosperm seeds the
most important components, together with
amphipods amongst hybrids (Table 2). This
greater importance of amphipods in hybrid
gullets was probably due to sampling bias
since, in the larger number of gizzards, the
percent occurrence of amphipods was similar
between stifftail species (Table 1).
The different biases inherent in each volumetric measure (see Discussion) were reflected
in marked differences between them (Table 2).
For example, angiosperm seeds were 12.5 times
more important than amphipods for all stifftails combined by aggregate percent, whereas
Table 2. Volumetric measurements of different food items in the gullets of Spanish stifftails.
All combined (29)
Plant
Angiosperm seeds
Charophyta (oospores)
Green plant material
Animal
Bryozoa
Polychaeta
Oligochaeta
Mollusca
Gastropoda
Crustacea
Ostracoda
Cladocera
Decapoda
Isopoda
Amphipoda
Insecta
Odonata
Corixidae
Aphididae
Chironomidae, larvae
Chironomidae, pupae
Other Diptera
Formicidae
Coleoptera
Unidentified insects
Unident. invertebrates
White-headed Duck (6)
Ruddy Duck (15)
Hybrids (8)
A
B
A
B
A
B
A
B
52.48
40.88
2.69
8.91
47.52
0.33
0.02
0.01
27.45
9.39
15.42
2.64
72.56
0.04
0.05
0.05
70.29
37.12
–
33.17
29.71
–
–
–
46.66
41.62
–
5.04
53.34
–
–
–
44.07
36.43
5.13
2.51
55.93
0.15
–
–
35.25
7.25
27.22
0.78
64.75
0.06
–
–
54.89
52.05
0.12
2.72
45.11
0.89
0.08
0.02
14.18
9.09
0.01
5.08
85.82
0.01
0.12
0.12
0.04
0.33
–
–
0.01
0.05
0.14
0.77
0.51
3.84
0.43
3.28
3.26
0.2
0.93
0.63
7.55
24.57
0.52
–
–
–
–
0.12
–
–
–
–
0.1
2.97
0.83
6.28
–
0.15
1.55
1.11
12.82
–
1.28
8.36
–
0.12
11.82
0.27
0.15
–
0.74
62.6
0.22
0.73
0.03
22.91
2.91
0.01
0.01
4.01
4.95
0.02
1.28
0.25
0.04
32.15
3.27
0.05
0.04
0.63
0.36
0.14
–
–
–
18.39
4.69
–
–
–
6.1
–
–
–
–
49.47
2.34
–
–
–
1.41
–
0.42
0.88
0.06
33.01
1.71
0.02
0.01
7.4
2.03
0.05
2.25
0.37
0.07
42.26
2.13
0.09
0.07
1.1
0.42
0.26
–
0.99
–
7.36
3.82
–
–
0.66
9.57
–
–
0.1
–
15.74
5.01
–
–
0.01
0.17
–
Values in parentheses = n. A, Mean of volumetric percentages (aggregate percent); B, percentage of total volume
(aggregate volume). The importance of soft-bodied invertebrates is underestimated in these data (see text).
© 2000 British Trust for Ornithology, Bird Study, 47, 275–284
Diet of Oxyura in Spain
Table 3. Index of Relative Importance (IRI) values for
major foods for stifftails in Spain, calculated for gullet
samples.a
Food
Downloaded by [CSIC Biblioteca] at 04:30 07 February 2012
Chironomidae
Angiosperm seeds
Green plant material
Unidentified invertebrates
Amphipoda
Charophyte oospores
Cladocera
Coleoptera
Isopoda
IRI
4223
3813
558
275
192
187
82
80
75
amphipods were 2.6 times more important than
seeds by aggregate volume. Animal matter
constituted 73% of aggregate volume, but only
48% of aggregate percent (Table 2). The IRI
values show that the Chironomidae were the
most important component of stifftail diet
in Spain, followed by seeds (Table 3). Both
components were more than six times as
important as other food items, although plant
material and crustaceans were of secondary
importance (Table 3).
DISCUSSION
In its native North America, benthic chironomid larvae are the most important food of the
Ruddy Duck in both sexes and at all times of
the year.21—24 One study in California found
Corixidae to be the most important food in
early and mid-winter.25 Plant food usually
constituted less than 20% of aggregate percent
in these studies. Benthic chironomids are also
the major component of Ruddy Duck diet
within the naturalized population in the UK
(B. Hughes et al. unpubl. data).
This paper provides the most detailed study
to date of the diet of White-headed Ducks. In
Spain, only three individuals have been studied
previously,26,27 in which chironomid larvae and
Potamogeton seeds were the most abundant
items. There are no quantitative data from
other parts of the range,28,29 although Whiteheaded Ducks were largely dependent on
benthic chironomids at their main wintering
site in Turkey30 and on polychaete worms at
one wintering site in Greece (authors’ unpubl.
data).
279
There are no previous reports of the diet of
White-headed Duck/Ruddy Duck hybrids.
With the exception of those collected from
wetlands in northern Spain (Fig. 1), feeding
Ruddy Ducks and hybrids intermixed and fed
together with much larger numbers of Whiteheaded Ducks. No differences in feeding
behaviour have been reported, and our results
support the view that there is little difference in
foraging strategies between the three taxa.
Thus, whilst it is not appropriate to collect the
globally threatened White-headed Duck,
Ruddy Ducks and hybrids shot as a conservation measure can be a useful indicator of food
selection by White-headed Ducks at the same
wetland.
Studies of diet in Anatidae are subject to
many different biases, e.g. differential digestion
of soft-bodied invertebrates compared to seeds
and other hard components of the diet.19,31,32
Ideal methods to reduce these biases involve
the selective collection of birds seen feeding for
at least 10 minutes, immediate extraction and
preservation of gullet contents, and exclusive
use of oesophagus contents with a minimum
volume (e.g. 0.1 ml) for volumetric analyses.24,33
Unfortunately, our sample was not collected
specifically for this analysis, feeding birds were
not selected and there were delays before gut
contents could be preserved. Owing to small
sample sizes, a volumetric analysis was done
on the combined gullet contents of 29 birds
without discarding those with a small volume
(59% of the gullet samples had a total volume
below 0.1 ml). Consequently, the seeds and
other plant material in stifftail diet were
over-represented in our results, particularly in
the aggregate percentages. In reality, chironomids were more dominant in the diet than
suggested by the IRI values (Table 3). Owing to
prior digestion, often only the relatively hard
headcases of chironomids remained in our
gullet samples, and the number and size of
headcases suggested that the volume of
chironomids ingested was at least 20% higher.
Nevertheless, seeds are undoubtedly important
in the diet of Spanish stifftails.
The relatively lower invertebrate diversity
recorded from White-headed Ducks probably
reflects the fact that most birds died from
disease or were dead for some time before
collection. The nine White-headed Ducks
found dead had fewer taxa in their gizzards
© 2000 British Trust for Ornithology, Bird Study, 47, 275–284
Downloaded by [CSIC Biblioteca] at 04:30 07 February 2012
280
M.I. Sanchez, A.J. Green and J.C. Dolz
than the eight birds shot (Mann—Whitney
U test: U = 58.5, P < 0.04). Our failure to detect
food selection differences between sexes, ages
and seasons probably reflects the limitations of
our small sample size and its highly heterogeneous nature (i.e. mixing of many years, sites
and processing methods). In North America,
Ruddy Ducks show sex and seasonal differences in diet.23,25
The nematodes found in gizzards of eight
birds during the breeding season may be
parasites rather than prey items. Five were
White-headed Ducks found dead, in four of
which nematodes were the only animals
present, suggesting they may have infested sick
or dead birds.
Chironomids tend to dominate the benthic
fauna in wetlands that undergo regular water
level fluctuations and in brackish rather than in
freshwater conditions.34—36 The lower chironomid frequency in Ruddy Duck and hybrid
gizzards from northern, temperate wetlands
may reflect their more freshwater, permanent
nature compared to the southern temporary
and brackish wetlands characteristic of the
Mediterranean region (Fig. 1). The difference
in salinity also explains the absence of polychaetes in northern samples.
In conclusion, White-headed Ducks and
exotic stifftails in Spain are highly dependent
on benthic chironomids throughout the annual
cycle. Benthic chironomids are relatively
tolerant of eutrophication.35 This in turn makes
White-headed Ducks more tolerant of wetland
eutrophication than many other waterbird
species (e.g. those dependent on submerged
macrophytes).37 Despite major wetland loss
and degradation in Spain in recent decades,38 a
major reduction in hunting mortality has
allowed the White-headed Duck population to
increase and expand across many wetlands in
the southern half of Spain in recent years.3,5 We
suggest that their ability to exploit abundant
chironomid resources has played an important
role in enabling this expansion. However, the
major dietary overlap observed between
White-headed Ducks, Ruddy Ducks and their
hybrids suggests that the expansion of Ruddy
Ducks across the White-headed Duck range
threatens the latter via competition as well as
by hybridization. This reinforces the need to
control the introduced populations of Ruddy
Ducks in Europe.6
© 2000 British Trust for Ornithology, Bird Study, 47, 275–284
ACKNOWLEDGEMENTS
This work was carried out with permission
from the Spanish White-headed Duck Working
Group and the regional and central administrations represented within it. We are grateful to
J.A. Amat, J. Cabot, C. Gerique, M. Gimenez,
M. Máñez, R. Mateo, P. Pereira and C. Urdiales
for their help in providing and dissecting the
birds, and to A. Gallardo, P. Garcia, C.M. Lopez
and J. Prenda for help in identifying gut contents.
Helpful comments on earlier versions of this
article were provided by J. Figuerola, A.D. Fox,
B. Hughes and an anonymous referee.
ENDNOTE
a. IRI = PC x [AV + API, where PC = percent
occurrence, AV = aggregate volume, AP = aggregate percentage. The IRI attempts to correct for
differential digestion rates and distortion of
volumes by combining all three measures to
identify important components of the diet.33
REFERENCES
1. Green, A.J. & Anstey, S. (1992) The status of the
White-headed Duck Oxyura leucocephala. Bird Conserv. Int., 2, 185–200.
2. Collar, N.J., Crosby, M.J. & Stattersfield, A.J. (1994)
Birds to Watch 2. The World List of Threatened Birds.
BirdLife Conservation Series No. 4. BirdLife International, Cambridge.
3. Torres, J.A. & Alcalá-Zamora, A. (1997) Seguimiento
de la población española de Malvasía Cabeciblanca
(Oxyura leucocephala) durante los años 1996 y
1997. Oxyura, 9, 85–99.
4. Green, A.J. (1999) Peak count for White-headed
Duck Oxyura leucocephala in Spain. Bird Conserv.
Int., 9, 284.
5. Green, A.J. & Hughes, B. (compilers) (1996) Action
Plan for the White-headed Duck Oxyura leucocephala in Europe. In Globally Threatened Birds in Europe.
Action Plans (eds B. Heredia, L. Rose & M. Painter),
pp. 119–145. Council of Europe Publishing, Strasbourg.
6. Hughes, B., Criado, J., Delany, S., Gallo-Ursi, U.,
Green, A.J., Grussu, M., Perennou, C. & Torres, J.A.
(1999) The status of the North American Ruddy Duck
Oxyura jamaicensis in the Western Palearctic:
towards an action plan for eradication. Report by the
Wildfowl & Wetlands Trust to the Council of Europe.
7. Torres, J.A. & Alcalá-Zamora, A. (1997) Evolución
temporal de la presencia de Malvasía Canela (Oxyu-
Downloaded by [CSIC Biblioteca] at 04:30 07 February 2012
Diet of Oxyura in Spain
ra jamaicensis) en España. Oxyura, 9, 45–52.
8. Argano, R. (1979) Isopodi (Crustacea Isopoda).
Guide per il riconoscimento delle specie animali delle
acque interne italiane, Vol. 5. Consiglio Nazionale
delle Ricerche, Verona.
9. Girod, A., Bianchi, I. & Mariani, M. (1980) Gasteropodi, 1 (Gastropoda: Pulmonata, Prosobranchia:
Neritidae, Viviparidae, Bithyniidae, Valvatidae).
Guide per il riconoscimento delle specie animali delle
acque interne italiane, Vol. 7. Consiglio Nazionale
delle Ricerche, Verona.
10. Giusti, F. & Pezzoli, E. (1980) Gasteropodi, 2 (Gastropoda: Prosobranchia: Hydrobioidea, Pyrguloidea).
Guide per il riconoscimento delle specie animali delle
acque interne italiane, Vol. 8. Consiglio Nazionale
delle Ricerche, Verona.
11. Campredon, S., Campredon, P., Pirot, J.Y. &
Tamisier, A. (1982) Manuel d’analyse des contenus
stomacaux de canards et de foulques. (Travail du
Centre d’Ecologie de Camargue). Office National de
la Chasse, Paris.
12. Richoux, P. (1982) Coléoptères aquatiques. Introduction pratique à la systématique des organismes des
eaux continentales francaises, Vol. 2. Association
Francaise de Limnologie, Paris.
13. Carchini, G. (1983) Odonati (Odonata). Guide per il
riconoscimento delle specie animali delle acque
interne italiane, Vol. 21. Consiglio Nazionale delle
Ricerche, Verona.
14. Tachet, H., Bournaud, M. & Richoux, P. (1987) Introduction à l’étude des macroinvertébrés des eaux
douces. Association Francaise de Limnologie, Paris.
15. Chinery, M. (1988) Guía de campo de los insectos de
España y de Europa. Ed. Omega, Barcelona.
16. Nieser, N., Baena, M., Martinez-Aviles, J. & Millan, A.
(1994) Claves para la identificación de los heterópteros acuáticos (nepomorpha & gerromorpha)
de la Península Ibérica. Asociación Española de
Limnología, Publicación No. 5, Madrid.
17. Alonso, M. (1998) Crustacea (Branchiopoda). Fauna
Ibérica, Vol. 7. Museo Nacional de Ciencias Naturales
y Consejo Superior de Investigaciones Científicas,
Madrid.
18. Nieto, J.M. & Mier, M.P. (1998) Hemiptera. Aphididae
I. Fauna Ibérica, Vol. 11. Museo Nacional de Ciencias
Naturales y Consejo Superior de Investigaciones
Científicas, Madrid.
19. Swanson, G.A., Krapu, G.L., Bartonek, J.C., Serie,
J.R. & Johnson, D.H. (1974) Advantages in mathematically weighting waterfowl food habits data. J.
Wildl. Manage., 38, 302–307.
20. Ayala, J.M., Matamala, J.J., López, J.M. & Aguilar,
F.J. (1994) Distribución actual de la Malvasía en
España. IWRB Threatened Waterfowl Research
Group Newsletter, 6, 8–11.
281
21. Hoppe, R.T., Smith, L.M. & Wester, D.B. (1986)
Foods of wintering diving ducks in South Carolina. J.
Field Ornithol., 57, 126–134.
22. Tome, M.W. & Wrubleski, D.A. (1988) Underwater
foraging behavior of canvasbacks, lesser scaups,
and ruddy ducks. Condor, 90, 168–172.
23. Woodin, M.C. & Swanson, G.A. (1989) Foods and
dietary strategies of prairie-nesting Ruddy Ducks and
Redheads. Condor, 91, 280–287.
24. Krapu, G.L. & Reinecke, K.J. (1992) Foraging ecology and nutrition. In Ecology and Management of
Breeding Waterfowl (eds B.D.J. Batt, A.D. Afton,
M.G. Anderson, C.D. Ankney, D.H. Johnson, J.A.
Kadlec & G.L. Krapu), pp. 1–29. University of Minnesota Press, Minneapolis.
25. Euliss, N.H., Jarvis, R.L. & Gilmer, D.S. (1997) Relationship between waterfowl nutrition and condition on
agricultural drainwater ponds in the tulare basin, California: waterfowl body composition. Wetlands, 17,
106–115.
26. Amat, J.A. & Sanchez, A. (1982) Biología y ecología
de la Malvasía Oxyura leucocephala en Andalucía.
Doñana Acta Vert., 9, 251–320.
27. Torres, J.A. & Arenas, R. (1985) Nuevos datos relativos a la alimentación de Oxyura leucocephala.
Ardeola, 32, 127–131.
28. Cramp, S., & Simmons, K.E.L. (1977) Handbook of
the Birds of Europe, Middle East & North Africa, Vol.
1. Oxford University Press, Oxford.
29. Anstey, S. (1989) The status and conservation of the
white-headed duck Oxyura leucocephala. IWRB
Special Publication, No. 10. IWRB, Slimbridge.
30. Green, A.J., Fox, A.D., Hughes, B. & Hilton, G.M.
(1999) Time-activity budgets and site selection of
White-headed Ducks (Oxyura leucocephala) at Burdur Lake, Turkey in late winter. Bird Study, 46, 62–73.
31. Sedinger, J.S. (1986) Biases in comparison of
proventricular and esophageal food samples from
Cackling Canada Geese. J. Wildl. Manage., 50,
221–222.
32. Swanson, G.A. & Bartonek, J.C. (1970) Bias associated with food analysis in gizzards of Blue-winged
Teal. J. Wildl. Manage, 34, 739–746.
33. Jeske, C.W., Percival, H.F. & Thul, J.E. (1993) Food
habits of Ringed-necked Ducks wintering in Florida.
Proc. Annu. Conf. Southeast. Assoc. Fish and Wildl.
Agencies, 47, 130–137.
34. Euliss, N.H. & Grodhaus, G. (1987) Management of
midges and other invertebrates for waterfowl wintering in California. Calif. Fish Game, 73, 238–243.
35. Batzer, D.P. & Wissinger, S.A. (1996) Ecology of
insect communities in nontidal wetlands. Ann. Rev.
Entom., 41, 75–100.
36. Green, A.J. & Hilton, G.M. (1998) Management procedures required to increase chironomid availability
© 2000 British Trust for Ornithology, Bird Study, 47, 275–284
282
M.I. Sanchez, A.J. Green and J.C. Dolz
to waders feeding on artificial lagoons remain
unclear. J. Appl. Ecol., 35, 9–12.
37. Green, A.J., Fox, A.D., Yarar, M., Hilton, G., Hughes,
B. & Salathe, T. (1996) Threats to Burdur Lake
ecosystem, Turkey and its waterbirds, particularly the
White-headed Duck Oxyura leucocephala. Biol. Conserv., 76, 241–252.
38. Casado, S. & Montes, C. (1995) Guía de los lagos y
humedales de España. Junta de Andalucía, Seville.
(MS received 18 October 1999; revised MS accepted 7 February 2000)
APPENDIX
Downloaded by [CSIC Biblioteca] at 04:30 07 February 2012
Taxonomic classification of food items recorded in stifftail guts, showing the number of individual ducks in which each
item was recorded
Food item
No. of ducks
Seeds
Polygonum spp
spp.
Suaeda spp.
Alisma spp.
Potamogeton pectinatus
Potamogeton pusillus
drepanensis
Ruppia spp.
Zannichellia spp.
Scirpus spp.
Eleocharis spp.
spp.
Trifolium spp.
Unidentified seeds
J(7) Atriplex
J(1), H(3)
L(1), J(3), H(1)
J(2)
L(9), J(17), H(12)
J(2), H(1) Ruppia
L(1), J(2), H(3)
L(10), J(14), H(21)
J(1), H(1)
L(10), J(13), H(10)
H(6) Phragmites
L(5), J(9), H(5)
L(1), J(6), H(2)
L(10), J(23), H(21)
Algae
F. Characeae, oospores
J(6), H(7)
Green plant material
L(15), J(20), H(21)
Invertebrates
Cl. Phylactolaemata (Bryozoa)
Plumatella repens, floatoblasts
Cristatella mucedo, floatoblasts
Cl. Insecta
O. Diptera
F. Chironomidae
SF. Chironominae
Tr. Chironomini
larvae
pupae
Unidentified chironominae, larvae
SF. Tanypodinae
larvae
pupae
SF. Orthocladinae, larvae
Unidentified chironomidae
larvae
pupae
J(4), H(2)
J(3)
L(6), J(11), H(12)
L(2), J(7), H(9)
L(1), J(8), H(4)
J(5), H(1)
J(1)
J(2)
L(8), J(11), H(14)
L(4), J(12), H(10)
L, White-headed Duck; J, Ruddy Duck; H, hybrid. Cl, class; O, order; F, family; SF, subfamily; Tr, tribe.
© 2000 British Trust for Ornithology, Bird Study, 47, 275–284
continued
Diet of Oxyura in Spain
283
APPENDIX continued
Downloaded by [CSIC Biblioteca] at 04:30 07 February 2012
Food item
F. Ceratopogonidae
SF. Ceratopogoninae, larvae
Unidentified ceratopogonidae
larvae
pupal case
F. Stratyomyidae
Nemotelus spp., larvae
F. Muscidae, pupal case
Unidentified diptera, larvae
O. Odonata
F. Libellulidae, larvae
Unidentified odonates, larvae
O. Coleoptera
F. Dytiscidae, adult
F. Hydrophilidae
Berosus spp., larvae
Unidentified coleoptera
larvae
adult
O. Hymenoptera
F. Formicidae, adult
O. Hemiptera
F. Corixidae, nymph
F. Aphididae, adult
Unidentified insects
adult
larvae
Cl. Crustacea
O. Podocopa
O. Cladocera
Daphnia spp.
ephippia
Eurycercus lamellatus
Unidentified cladocera
O. Decapoda
O. Amphipoda
Echinogammarus spp.
clutch
Unidentified amphipods
O. Isopoda
Sphaeroma hookeri
O. Cyclopoida
Cyclops spp
Unidentified crustacea
Cl.Arachnida
O. Acarina
Cl. Annelida
O. Polychaeta
O. Oligochaeta
F. Lumbricidae
Unidentified oligochaeta
O. Achaeta
No. of ducks
J(2), H(1)
J(2), H(1)
L(1), J(1)
J(1)
J(1), H(1)
H(2)
J(1)
L(1), J(5), H(3)
J(1)
J(2)
J(1)
L(7), J(13), H(11)
L(1), J(2), H(1)
L(2), J(8), H(2)
J(1)
L(10), J(20), H(11)
J(7), H(3)
L(2), J(6), H(4)
J(1), H(1)
L(3), J(8), H(10)
J(1)
J(2), H(2)
J(4), H(2)
J(2), H(2)
J(2), H(3)
L(1), J(1)
J(1), H(1)
H(1)
L(1), J(3), H(2)
H(1)
J(2), H(5)
J(1)
H(1)
L, White-headed Duck; J, Ruddy Duck; H, hybrid. Cl, class; O, order; F, family; SF, subfamily; Tr, tribe.
continued
© 2000 British Trust for Ornithology, Bird Study, 47, 275–284
284
M.I. Sanchez, A.J. Green and J.C. Dolz
APPENDIX continued
Food item
No. of ducks
F. Hirudidae
Phylum Nematoda
Cl. Gastropoda
F. Hydrobiidae
Physidae
Unidentified gastropods
Cl. Bivalvia
Unidentified invertebrates
Unidentified invertebrate eggs
J(1), H(1)
L(6), J(1), H(1)
H(4) F.
J(1)
L(2), J(5), H(6)
J(5), H(5)
L(3), J(1), H(1)
L(1), J(5), H(2)
Downloaded by [CSIC Biblioteca] at 04:30 07 February 2012
L, White-headed Duck; J, Ruddy Duck; H, hybrid. Cl, class; O, order; F, family; SF, subfamily; Tr, tribe.
© 2000 British Trust for Ornithology, Bird Study, 47, 275–284